In U.S. Pat. No. 4,052,446, Holland et al., prostaglandins of the formula: ##STR1##
wherein R is hydrogen or lower alkyl, R.sub.1 is lower alkyl,
R.sub.9 is hydrogen or lower alkyl; R.sub.9 ' is hydrogen, lower alkyl or fluoro
useful as antisecretory agents for preventing hyperacidity. Also, this patent discloses the protection of the 15-hydroxy group when the compound of formula II is formed by oxidation of the corresponding 11-hydroxy compound of the formula: ##STR2##
wherein R, R.sub.6, R.sub.9 and R.sub.9 ' are as above and R.sub.6 is hydroxy protected with a hydrolyzable ether and ester group.